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<h1 id="dc--operating-point-analysis">DC / Operating point analysis</h1>

<h2 id="operating-point-calculations">Operating point calculations</h2>
<p>The operating point of a circuit is the static solution to a a circuit, ie. all voltages and currents are assumed to be constant over time.</p>
<p align="center"><img src="images/operatingpoint.svg"></p>

<p>Calculating the operating point is often the first step in any simulation. First the temperature-dependent properties are calculated. Then the analysis will <strong><a href="iterate.html">iterate</a></strong> to find a solution. Iterative solutions do not always guarantee convergence, so multiple schemes are provided to help convergence if the first attempt fails.</p>
<h2 id="gmin-stepping">Gmin stepping</h2>
<p>A common issue for convergence is exponential dependencies of a current on a voltage or vice-versa, like is often the case in diode-type structures (PN-junctions). The problem occurs because on one side of the exponential the curve is very horizontal, while on the other side it is almost vertical. This causes iteration to either over-step (when on the horizontal side), or to under-step (when on the vertical side) when the current solution is too far from the actual solution. By placing an additional resistive path in parallel to these problematic areas this issue can be alleviated. First a high <strong>Gmin</strong> allows the circuit to converge pretty quickly to a solution that is closer to the actual solution. This new solution can be used to iterate again with progressively smaller <strong>Gmin</strong> as the solution gets closer and closer to the actual solution.</p>
<h2 id="diagonal-gmin-stepping">Diagonal Gmin stepping</h2>
<p>Diagonal Gmin stepping is almost identical to Gmin stepping, except that it will add a resistor to <strong>ground</strong> from each node in the circuit, not just for exponential curves. This translates to adding <strong>Gmin</strong> to each diagonal element of a voltage node in the Y-matrix - hence the name.</p>
<h2 id="source-stepping">Source stepping</h2>
<p>For source stepping, all independent sources are given a value of 0 volts or 0 amps. The solution should at that point be trivial (all voltages and currents will be very close to 0). By slowly ramping up the independent sources again, a solution can be found where the solution does not change as much from one step to the next.</p>
<h1 id="dc-analysis">DC analysis</h1>
<p>A DC analysis is nothing more than a sequence of operating point analysis where one or more parameters are being swept.</p>
<p>Temperature-dependent calculations are executed only once at the start of the sweep.</p>
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